1. Field of the Invention
In conventional radar sytems in which a volume in space is scanned and a mean level detector is utilized to apply signals to an azimuth integrator, large azimuth errors for detected targets are produced in the presence of external noise sources such as broad band noise jammers. This is caused by the azimuth integrating filter responding to the noise to cause substantial errors in the target azimuth estimation. Also, the difficulty of detecting targets in the presence of noise or noise jamming results in a highly variable noise false alarm rate. Some other problems associated with the operation of the conventional mean level detector are that it is relatively complex to implement (requiring a moving window memory in the range dimension) and that its accuracy is limited because valid targets contribute to the sample mean.
2. Description of the Prior Art
The prior art is adaptive mean level thresholding systems such as described by G. M. Dillard in "Mean Level Detection of Non-Fluctuating Signals", IEEE Trans. on Aerospace and Electronic Systems, Vol. AES-10, No. 6 November, 1974, pages 795-799. This paper describes the conventional mean level processor which uses a moving window in range for the accumulator and does not provide for exclusion of valid targets from the sample mean. Other prior art approach uses a ranking technique to exclude some, but not all, valid targets from the sample mean such as described by J. T. Rickard and G. M. Dillard, "Adaptive Detection Algorithms for Multiple-Target Situations", IEEE Trans. Aerospace and Electronic System, AES-13, June, 1977, pages 338-343. Thus, these prior art systems do not provide an arrangement that will satisfactorily estimate the background noise level and provide a constant false alarm rate (CFAR) when valid targets are present.